In various technological fields the rotation of a shaft is sensed. Various control functionality may rely on the sensed rotation of the shaft. E.g., a rotational speed or angular velocity of a shaft of a transmission may be used to control the operation of the transmission. E.g., an angular velocity of a shaft of a wheel axle may be used to monitor friction of the corresponding wheel; this may be useful for antiblocking systems or electronic stability systems in vehicles.
A known way of sensing rotation of the shaft is to place a ferromagnetic toothed wheel on the shaft and use a sensor to detect passing of teeth of the toothed wheel. Typically, the sensor is placed at a distance from the rotational axis of the shaft; often, the sensor is placed radially offset from the ferromagnetic toothed wheel. The output of such sensor typically corresponds to a pattern of pulses in which the frequency of pulses varies according to the speed of rotation. By giving the different teeth of the toothed wheel a size which is distinctive with respect to other teeth of the toothed wheel, it becomes also possible to distinguish between different angular positions in the course of a single rotation of the shaft. It is for example conceivable to make just one of the teeth different from the other, so that an angular position of the toothed wheel may be identified. Without any limitation, more than one of the teeth may be made identifiable whereby more than one of the angular positions are made identifiable.
However, evaluation of the rotation angle using such toothed wheel requires that the shaft is actually rotating. Sometimes, at least one full rotation is needed to determine the absolute orientation. Further, complex algorithms may be needed for accurately estimating the rotation angle from the sensed pattern of pulses. Also, the achievable accuracy may significantly depend on a manufacturing accuracy of the toothed wheel as well as a precision in mounting the sensor relative to the toothed wheel. Still further, the toothed wheels—sometimes also referred to as magnetic encoder wheels—may require significant space and may be comparably expensive.
Accordingly there is a need for techniques which allow for sensing rotation of a shaft in an efficient and accurate manner.